The present invention relates generally to a magnetic erasing head for use in a magnetic recording and reproducing apparatus, and more particularly, to a magnetic erasing head which is easy to be fabricated and which further exhibits good erasing characteristics in erasing signals recorded on a metal tape having large coercive force.
Several types of magnetic erasing head for use in magnetic recording and reproducing apparatuses have been developed. Among these previously developed types is a magnetic erasing head which has two gaps and is known as the double-gap type. This widely used double-gap arrangement provides good magnetic erasing characteristics.
In the double-gap type magnetic erasing head, the opposite lateral sides of an I-shaped core accommodated within a coil, have bonded thereto a pair of C-shaped cores with spaces for forming gaps interposed therebetween. Since this known magnetic erasing head, however, comprises the above-mentioned three core members, two unnecessary rear gaps are inevitably formed between the I-shaped core and the C-shaped cores at the rear side thereof, in addition to the front gaps which normally serve as erasing gaps. The two rear gaps develop large magnetic resistance and thereby large losses. Accordingly, this magnetic head gives rise to a problem of not carrying out the erasing operation with good efficiency.
Moreover, since the above-mentioned magnetic erasing head is assembled by fabricating three separate cores, great care must be taken during assembly in aligning the height of each core in the track width direction. This gives rise to difficulty of assembly and poor working efficiency.
All of these cores are made of ferrite. General ferrite used heretofore includes high-density ferrite composed to NiO (11% by weight), ZnO (22%) and Fe.sub.2 O.sub.3 (67%), single crystal ferrite composed of MnO (23%), ZnO (7%) and Fe.sub.2 O.sub.3 (70%), one hot-press ferrite composed of MnO (15%), ZnO (15%) and Fe.sub.2 O.sub.3 (70%), another hot-press ferrite composed of NiO (18.9%), ZnO (13.6%) and Fe.sub.2 O.sub.3 (67.5%), one sintered ferrite composed of NiO (19%), ZnO (13.5%) and Fe.sub.2 O.sub.3 (67.5%), and another sintered ferrite composed of MnO (26.22 parts by weight), ZnO (20.98), Fe.sub.2 O.sub.3 (52.8) and CaCO.sub.3 (0.005).
These ferrite materials, however, show a saturated flux density smaller than that of a magnetic metal material such as iron-silicon-aluminum alloy (so-called sendust alloy, and referred to as "sendust"). Accordingly, a difficulty arises in that the magnetic erasing head consisting of cores made of the above described ferrite materials is not capable of performing erasing operations fully with respect to a metal tape coated with pure iron powder and showing extremely high coercive force up to 1,000 to 1,200 oersted (Oe).
Another example known heretofore, there can be mentioned a magnetic erasing head having core chips made of sendust bonded to the I-and C-shaped permalloy cores at their distal ends. This head is used in place of the above-described I- and C-shaped ferrite cores and is fabricated in the same manner as described above.
This known example also has disadvantages such as difficulty of fabrication. In addition, when a large erasing current is passed therethrough in order to fully carry out erasing action with respect to the metal tape, the eddy currents induced become too large to be ignored and cause a large temperature rise in the head. Therefore, this magnetic head cannot be adapted to erasure of metal tapes.